The broad, long term goal of Project 3 is to compare the ex vivo efficacy and safety of film vs gel formulations pf two antiretroviral drugs being developed as topical microbicides. The overarching hypothesis is that gel and film formulations of tenofovir and UC781 will have efficacy agaist HIV in tissue explants from women exposed to these formulations, but there will be a differential impact of the two dosage forms on the vaginal ecology including genital mucus. Over the five year period, we will 1) establish the ex vivo HIV challenge model in biopsy samples, 2) compare the protective effect of vaginal gel and film formulations of tenofovir and UC781 against HIV in the ex vivo challenge model, 3) compare the effects of gel and film formulations of tenofovir and UC781 on the vginal ecology and 4) measure the levels of tenofovir and UC781 in the cervicovaginal lavage and blood samples obtained from women enrolled in the two Exploratory IND studies described in this project. For Aim 1, the ex vivo challenge model for ectocervical and vaginal biopsy samples will be developed in 20 volunteers during year 1. Two randomized, placebo-controlled trials comparing gel to film formulations of tenofovir and UC781 will be conducted in years 2-5 of the project period. These study populations will provide ectocervical biopsy tissue for evaluation of product efficacy against HIV ex vivo (Core B), as well as multiple measures of product safety and pharmacokinetic assessment of drug levels in blood and cervicovaginal lavage (Project 4). The impact of gel and film products on innate immunity of the female genital tract will be assessed by measuring innate antiviral and antibacterial activity of vaginal fluid before and after product exposure, assessment of the vaginal microflora, and measurement of innate immune mediators. Mucus and mucin-degrading enzymes present in the vaginal fluid before and after product exposure will be compared. At the conclusion of these studies, film formulations of UC781 and tenofovir will be posed to enter formal Phase 1 safety studies. This project relies on Project 4, Core A, Core B and Core C.